<div class="demo-step">
  <div class="demo-step-up" [ngStyle]="{'margin-left':'calc('+percent+'% - 4px)'}"></div>
  <div class="demo-step-middle">
    <div class="demo-step-left"></div>
    <div class="demo-step-center"></div>
    <div class="demo-step-right"></div>
  </div>
  <div class="demo-step-down" [ngStyle]="{'margin-left':'calc('+percent+'% - 4px)'}"></div>
</div>
